*Spoilers* Han Seo Jun and Ji-Eun had...

It's all a bit contrived. Han Seo Jun's wife met another pregnant mother in the lobby of Dr. Daniel Lee's office in episode 1, I believe. This woman was also carrying a baby with the gene that had a chance of being 99% psychopath or 1% genius. The two mothers decided to switch babies so if either of the children started displaying violent behavior it would be easier for the non-birth mother to kill the child, as opposed to simply getting the child some help, which is what people in the real world would do. So Han Seo Jun's wife had the other woman's son, Yohan, and the other woman had Jung Ba Reum who was Han Seo Jun's son. Yo Han, therefore, wound up taking the abuse and butt-kickings for being the son of serial killer Han Seo Jun when he was not only not Han Seo Jun's son, he didn't even have the psychopath gene. He had the genius gene. Of course, Ji-Eun, Han Seo Jun's wife kept her mouth shut even when Jung Ba Reum (Jae Hoon at the time) was killing and cutting up rabbits at school (Yo Han and Jae Hoon were classmates and knew each other so it seems unlikely that Ji-Eun would have remained ignorant of this) and even maintained her silence when Jung Ba Reum's pseudo-family was killed and his house set on fire and people suspected Jung Ba Reum was involved. This is why it is so contrived. You give your natural son away so the adoptive mother can kill him if need be, but don't say boo to a goose when his adoptive family comes up brutally murdered. You just go on with the son you took in and hope all turns out for the best. Doesn't make much sense. There's a lot of that in this drama. Things that the screenwriter used to further the plot that make absolutely no sense. If you want the viewer to buy that JBR got part of YH's frontal lobe and that has suddenly given him moral capacity and empathy, I think the viewers are willing to suspend disbelief that much. It's a stretch, but we'll play along. But when you start coming up with all these crazy scenarios: multiple orphans, multiple serial killers all interacting with the same people, children being switched for dumb reasons, police finding the body of the police detective's daughter and not even doing DNA tests on the bones, Chi Kook not telling the police that it was JBR that tried to kill him, the priest not telling the television audience who had a knife at his throat (he knew he was going to die and even if he was willing to forgive JBR for killing him, he had to know how dangerous he was and how many other people would be endangered by his silence--including his detective brother), this whole organization of OZ that is willing to observe JBR killing people (and clean up behind his murders) to "make the world a better place", Dr. Lee nearly being killed by OZ but then resurfacing to interact with serial killer JBR so he can get him to kill other people, Ji-Eun losing her grandson but not telling his mother? not telling the other police that the detective was holding the baby hostage? It's all completely crazy. It's as if the screenwriter had a destination in mind and didn't care what preposterous detours it would take to get there. This drama had so much promise the first 10 episodes. It really is terrible to see what it devolved into. Lee Seung Gi worked so hard on this. He poured so much energy, mental, physical and emotional into this. I wish it had remained worthy of him. I'm glad it's getting good ratings, I think that's a testament to his acting and to the excellence of the first 10 episodes. 

 mary:

thankyou for clearing it up,also 100% agree that the plot after the 1st 10 eps was going way off track,up till the first 10 eps i was glued to my screen watching it no matter what the time was and was on my toes at all times because of the growing suspense but after these eps i started to lose interest and would skip or forward a lot of parts since all the plot holes and loops you mentioned surfaced my mind too,lots of things dont have solid reasoning or backing and make it seem like the writer just wanted to add in whatever after the 10 episode mark

You are welcome! Well, I think you mean other comments here. I personally disagree about skipping the parts because this is the kind of drama that needs close attention. Fast-forwarding can cause skipping the important parts like these baby swapping etc. So even the parts that explain in drama can seem like plot holes. And especially in the last couple of episodes, they explain a lot of things with references to the first episodes.